pyelftools: Add DIR_METADATA.

- Use same DIR_METADATA as chromite.

- Also fix OWNERS (it was referring to a branch that doesn't
exist on chromite, so there were no OWNERS).

BUG=None
TEST=CQ

Change-Id: I771cd59816c38faf6dbadc7cbff2f6ef5ab52a5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/pyelftools/+/4245677
Owners-Override: Ram Chandrasekar <rchandrasekar@google.com>
Reviewed-by: Navil Perez <navil@google.com>
Auto-Submit: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Commit-Queue: Navil Perez <navil@google.com>